Download Section 11.3(student copy)

Section 11.3
Factors That Regulate
Natural Populations
Density-Independent Factors

________________________________
________________________________
________________________________

Ex. Floods, droughts, etc…

Abiotic
Density-Dependent Factors

________________________________
________________________________
________________________________

Competition, predation

Biotic
What is a Community?

A biological community
All _____________________ in a given
ecosystem at
a given time.

Ecological Niche

The ecological niche

Is the total of an organism’s use of the
_______________ and _____________
resources in its environment

Habitat = organism’s “address”

Niche = organism’s
“_________________”

Fundamental Niche

The biological characteristics of the
organism and the set of resources
individuals in the population are
__________________________ capable
of using under ______________
conditions.

Realized Niche

The biological characteristics of the
organism and the resources individuals in
a population ____________________use
under the prevailing conditions
Interactions Between Species

3 Main Types



1. Competition
2. Predation
3. Symbiosis

_________________________________

_________________________________

_________________________________
Intraspecific Competition


A situation in which members of the
_____________ population complete
for resources
Ex. Wood bison competing for food
Interspecific Competition

Occurs when ___________________species
compete for a particular resource that is in
short supply

Two Types:


Interference competition - aggression between
individuals fighting over the same resource(s)
Exploitative competition - consumption of resource
by one species may limit resource availability to
other species
Results of Competition:



Population of weaker species
__________________________
One species changes behaviour to use
_____________________ resources
__________________ to another
habitat where resources are more
plentiful

Interspecific Competition

Driving force for populations of species to
evolve _______________________ to
allow them to use alternate resources for
continued survival.
Resource Partitioning

Resource partitioning is the
differentiation of niches


That enables similar species to
_____________ in a community
Ex. Several species of Anolis lizard use
different parts of the tree habitats by
occupying different perching sites
Example:
A. insolitus
usually perches
on shady branches.
A. ricordii
A. insolitus
A. distichus perches
on fence posts and
other sunny surfaces.
A. alinigar
A. christophei
A. distichus
A. cybotes
A. etheridgei
Character Displacement


There is a tendency for characteristics to be
more divergent in populations of two species
that occupy the same geographical range than
in populations of the same two species that
are geographically isolated.
Example: Experiments with barnacle species
Predation

Predation refers to an interaction



Where one species, the predator, kills and
eats the other, the prey
Some predator-prey relationships
display a __________________ pattern
Predator patterns ____________
behind the prey patterns

Ex. Lynx-Hare
Adaptation of Predators/Prey

Feeding adaptations of predators
include


Claws, teeth, fangs, stingers, and poison
Animals also display

A great variety of defensive adaptations
Defence Mechanisms

Cryptic/Protective colouration, or
camouflage

Makes prey difficult to spot

Aposematic
coloration

Warns predators to
stay away from prey
Mimicry


In some cases, one prey species may
gain significant protection by mimicking
the appearance of another
Two types:


Batesian mimicry
Mullerian mimicry
In Batesian mimcry

A palatable
or harmless
species
mimics an
unpalatable
or harmful
model
(b) Green parrot snake
(a) Hawkmoth larva
In Müllerian mimicry
Two or more unpalatable species
resemble each other
(a) Cuckoo bee
(b) Yellow jacket
Symbiosis




Means “________________________”
Individuals of two different species live
in close (usually physical) contact
At least one species ______________
from the relationship
3 types:

mutualism, commensalism and parasitism
Mutualism

Mutualistic symbiosis, or mutualism

Is an interspecific interaction that benefits
_______________ species

Ex. Bacteria that live in the gut of cows, deer and
sheep



Bacteria secrete enzymes to break down cellulose for
herbivores
Bacteria gain nutrients for themselves
Called: obligatory mutualism

Neither can grow or reproduce without the other
Commensalism

In commensalism

One species _______________ and the
other is not __________________

Ex. Caribou and artic foxes


Artic fox follow caribou tracks, which uncover small
mammals
Ex. Remora (small fish) and sharks

Remora attach themselves to sharks – do not
expend energy swimming, receive protection and
feed on small pieces of the lemon shark’s prey
Parasitism



A symbiotic relationship in which one
organism (the parasite)
______________ at the
___________________ of another
organisms (host)
Host is often harmed, but not usually
killed
Examples: tapeworms, ticks
Types of Parasites



Endoparasites: parasites that live and feed
within the host’s body (ex. tapeworms that
live inside digestive tracts)
Ectoparasites: parasites that live and feed on
the outside surface of the host, such as lice,
ticks and parasitic mites
Social parasites: parasites that complete their
life cycle by manipulating the social behaviour
of their hosts (ex. cowbirds that lay eggs in
smaller birds nests)
Disruption of Community
Equilibrium

A natural disaster


Can break down intrinsic interactions among
communities organisms
Introduction of exotic (non-indigenous)
species




Displace indigenous species from community
Often have few predators
Out compete indigenous species for food and
habitat
Prey on indigenous species
Introduction of Exotic Species




Example: Introduction of European rabbit in
Australia (1859)
Breed rapidly - within decades there were
tens of millions of rabbits
Devastated grasslands, deprived indigenous
species of food, water and shelter
Introduced virus that selectively targeted
rabbits and managed to bring them under
control
Other Examples of Exotic
Species




Purple Loosestrife
African Killer Bees
West Nile Virus
Zebra Mussels